Return StackFuture instead of Box for async trait methods

Cargo.toml

@@ -1,16 +1,16 @@
 [package]
-name = "async-trait"
-version = "0.1.57"
-authors = ["David Tolnay <dtolnay@gmail.com>"]
+name = "stackfuture-async-trait"
+version = "0.1.0"
+authors = ["David Tolnay <dtolnay@gmail.com>", "Eric Holk <ericholk@microsoft.com>"]
 categories = ["asynchronous", "no-std"]
 description = "Type erasure for async trait methods"
-documentation = "https://docs.rs/async-trait"
-edition = "2018"
+documentation = "https://docs.rs/stackfuture-async-trait"
+edition = "2021"
 keywords = ["async"]
 license = "MIT OR Apache-2.0"
 readme = "README.md"
-repository = "https://github.com/dtolnay/async-trait"
-rust-version = "1.39"
+repository = "https://github.com/eholk/stackfuture-async-trait"
+rust-version = "1.56"
 
 [lib]
 proc-macro = true
@@ -23,6 +23,7 @@ syn = { version = "1.0.96", features = ["full", "visit-mut"] }
 [dev-dependencies]
 futures = "0.3"
 rustversion = "1.0"
+stackfuture = "0.2.0"
 tracing = "0.1.14"
 tracing-attributes = "0.1.14"
 trybuild = { version = "1.0.49", features = ["diff"] }

README.md

@@ -1,10 +1,10 @@
 Async trait methods
 ===================
 
-[<img alt="github" src="https://img.shields.io/badge/github-dtolnay/async--trait-8da0cb?style=for-the-badge&labelColor=555555&logo=github" height="20">](https://github.com/dtolnay/async-trait)
-[<img alt="crates.io" src="https://img.shields.io/crates/v/async-trait.svg?style=for-the-badge&color=fc8d62&logo=rust" height="20">](https://crates.io/crates/async-trait)
-[<img alt="docs.rs" src="https://img.shields.io/badge/docs.rs-async--trait-66c2a5?style=for-the-badge&labelColor=555555&logo=docs.rs" height="20">](https://docs.rs/async-trait)
-[<img alt="build status" src="https://img.shields.io/github/workflow/status/dtolnay/async-trait/CI/master?style=for-the-badge" height="20">](https://github.com/dtolnay/async-trait/actions?query=branch%3Amaster)
+[<img alt="github" src="https://img.shields.io/badge/github-eholk/async--trait-8da0cb?style=for-the-badge&labelColor=555555&logo=github" height="20">](https://github.com/eholk/stackfuture-async-trait)
+[<img alt="crates.io" src="https://img.shields.io/crates/v/stackfuture-async-trait.svg?style=for-the-badge&color=fc8d62&logo=rust" height="20">](https://crates.io/crates/stackfuture-async-trait)
+[<img alt="docs.rs" src="https://img.shields.io/badge/docs.rs-async--trait-66c2a5?style=for-the-badge&labelColor=555555&logo=docs.rs" height="20">](https://docs.rs/stackfuture-async-trait)
+[<img alt="build status" src="https://img.shields.io/github/workflow/status/eholk/stackfuture-async-trait/CI/master?style=for-the-badge" height="20">](https://github.com/dtolnay/stackfuture-async-trait/actions?query=branch%3Amaster)
 
 The initial round of stabilizations for the async/await language feature in Rust
 1.39 did not include support for async fn in traits. Trying to include an async
@@ -32,7 +32,10 @@ deliver in the future.
 
 [hard]: https://smallcultfollowing.com/babysteps/blog/2019/10/26/async-fn-in-traits-are-hard/
 
-<br>
+This is a fork of <https://github.com/dtolnay/async-trait> that has been modified to use [StackFuture]
+instead of boxing the futures returned by async trait methods.
+
+[StackFuture]: https://crates.io/crates/stackfuture
 
 ## Example
 

src/args.rs

@@ -1,36 +1,46 @@
 use proc_macro2::Span;
 use syn::parse::{Error, Parse, ParseStream, Result};
-use syn::Token;
+use syn::{Expr, Token};
 
-#[derive(Copy, Clone)]
+#[derive(Clone)]
 pub struct Args {
     pub local: bool,
+    pub stack_size: Expr,
 }
 
 mod kw {
     syn::custom_keyword!(Send);
 }
 
 impl Parse for Args {
-    fn parse(input: ParseStream) -> Result<Self> {
+    fn parse(input: ParseStream<'_>) -> Result<Self> {
         match try_parse(input) {
             Ok(args) if input.is_empty() => Ok(args),
             _ => Err(error()),
         }
     }
 }
 
-fn try_parse(input: ParseStream) -> Result<Args> {
-    if input.peek(Token![?]) {
+fn try_parse(input: ParseStream<'_>) -> Result<Args> {
+    let stack_size = input.parse()?;
+
+    if input.peek(Token![,]) {
+        input.parse::<Token![,]>()?;
         input.parse::<Token![?]>()?;
         input.parse::<kw::Send>()?;
-        Ok(Args { local: true })
+        Ok(Args {
+            local: true,
+            stack_size,
+        })
     } else {
-        Ok(Args { local: false })
+        Ok(Args {
+            local: false,
+            stack_size,
+        })
     }
 }
 
 fn error() -> Error {
-    let msg = "expected #[async_trait] or #[async_trait(?Send)]";
+    let msg = "expected #[async_trait(SIZE)] or #[async_trait(SIZE, ?Send)]";
     Error::new(Span::call_site(), msg)
 }

src/expand.rs

@@ -8,7 +8,7 @@ use std::mem;
 use syn::punctuated::Punctuated;
 use syn::visit_mut::{self, VisitMut};
 use syn::{
-    parse_quote, parse_quote_spanned, Attribute, Block, FnArg, GenericParam, Generics, Ident,
+    parse_quote, parse_quote_spanned, Attribute, Block, Expr, FnArg, GenericParam, Generics, Ident,
     ImplItem, Lifetime, LifetimeDef, Pat, PatIdent, Receiver, ReturnType, Signature, Stmt, Token,
     TraitItem, Type, TypeParamBound, TypePath, WhereClause,
 };
@@ -53,7 +53,7 @@ impl Context<'_> {
 
 type Supertraits = Punctuated<TypeParamBound, Token![+]>;
 
-pub fn expand(input: &mut Item, is_local: bool) {
+pub fn expand(input: &mut Item, is_local: bool, stack_size: &Expr) {
     match input {
         Item::Trait(input) => {
             let context = Context::Trait {
@@ -75,7 +75,7 @@ pub fn expand(input: &mut Item, is_local: bool) {
                             method.attrs.push(lint_suppress_without_body());
                         }
                         let has_default = method.default.is_some();
-                        transform_sig(context, sig, has_self, has_default, is_local);
+                        transform_sig(context, sig, has_self, has_default, is_local, stack_size);
                     }
                 }
             }
@@ -108,7 +108,7 @@ pub fn expand(input: &mut Item, is_local: bool) {
                         let block = &mut method.block;
                         let has_self = has_self_in_sig(sig) || has_self_in_block(block);
                         transform_block(context, sig, block);
-                        transform_sig(context, sig, has_self, false, is_local);
+                        transform_sig(context, sig, has_self, false, is_local, stack_size);
                         method.attrs.push(lint_suppress_with_body());
                     }
                 }
@@ -153,11 +153,12 @@ fn lint_suppress_without_body() -> Attribute {
 //         T: 'async_trait,
 //         Self: Sync + 'async_trait;
 fn transform_sig(
-    context: Context,
+    context: Context<'_>,
     sig: &mut Signature,
     has_self: bool,
     has_default: bool,
     is_local: bool,
+    stack_size: &Expr,
 ) {
     sig.fn_token.span = sig.asyncness.take().unwrap().span;
 
@@ -289,15 +290,9 @@ fn transform_sig(
     }
 
     let ret_span = sig.ident.span();
-    let bounds = if is_local {
-        quote_spanned!(ret_span=> 'async_trait)
-    } else {
-        quote_spanned!(ret_span=> ::core::marker::Send + 'async_trait)
-    };
+    let bounds = quote_spanned!(ret_span=> 'async_trait);
     sig.output = parse_quote_spanned! {ret_span=>
-        -> ::core::pin::Pin<Box<
-            dyn ::core::future::Future<Output = #ret> + #bounds
-        >>
+        -> ::stackfuture::StackFuture<#bounds, #ret, #stack_size>
     };
 }
 
@@ -318,7 +313,7 @@ fn transform_sig(
 //
 //         ___ret
 //     })
-fn transform_block(context: Context, sig: &mut Signature, block: &mut Block) {
+fn transform_block(context: Context<'_>, sig: &mut Signature, block: &mut Block) {
     if let Some(Stmt::Item(syn::Item::Verbatim(item))) = block.stmts.first() {
         if block.stmts.len() == 1 && item.to_string() == ";" {
             return;
@@ -397,7 +392,7 @@ fn transform_block(context: Context, sig: &mut Signature, block: &mut Block) {
         }
     };
     let box_pin = quote_spanned!(block.brace_token.span=>
-        Box::pin(async move { #let_ret })
+        ::stackfuture::StackFuture::from(async move { #let_ret })
     );
     block.stmts = parse_quote!(#box_pin);
 }
@@ -426,7 +421,7 @@ fn has_bound(supertraits: &Supertraits, marker: &Ident) -> bool {
     false
 }
 
-fn contains_associated_type_impl_trait(context: Context, ret: &mut Type) -> bool {
+fn contains_associated_type_impl_trait(context: Context<'_>, ret: &mut Type) -> bool {
     struct AssociatedTypeImplTraits<'a> {
         set: &'a Set<Ident>,
         contains: bool,

src/lib.rs

@@ -41,20 +41,20 @@
 //! This example implements the core of a highly effective advertising platform
 //! using async fn in a trait.
 //!
-//! The only thing to notice here is that we write an `#[async_trait]` macro on
+//! The only thing to notice here is that we write an `#[async_trait(512)]` macro on
 //! top of traits and trait impls that contain async fn, and then they work.
 //!
 //! ```
-//! use async_trait::async_trait;
+//! use stackfuture_async_trait::async_trait;
 //!
-//! #[async_trait]
+//! #[async_trait(512)]
 //! trait Advertisement {
 //!     async fn run(&self);
 //! }
 //!
 //! struct Modal;
 //!
-//! #[async_trait]
+//! #[async_trait(512)]
 //! impl Advertisement for Modal {
 //!     async fn run(&self) {
 //!         self.render_fullscreen().await;
@@ -69,7 +69,7 @@
 //!     media_url: String,
 //! }
 //!
-//! #[async_trait]
+//! #[async_trait(512)]
 //! impl Advertisement for AutoplayingVideo {
 //!     async fn run(&self) {
 //!         let stream = connect(&self.media_url).await;
@@ -163,11 +163,11 @@
 //! error message.
 //!
 //! ```compile_fail
-//! # use async_trait::async_trait;
+//! # use stackfuture_async_trait::async_trait;
 //! #
 //! type Elided<'a> = &'a usize;
 //!
-//! #[async_trait]
+//! #[async_trait(512)]
 //! trait Test {
 //!     async fn test(not_okay: Elided, okay: &usize) {}
 //! }
@@ -184,16 +184,16 @@
 //! The fix is to name the lifetime or use `'_`.
 //!
 //! ```
-//! # use async_trait::async_trait;
+//! # use stackfuture_async_trait::async_trait;
 //! #
 //! # type Elided<'a> = &'a usize;
 //! #
-//! #[async_trait]
+//! #[async_trait(512)]
 //! trait Test {
 //!     // either
 //!     async fn test<'e>(elided: Elided<'e>) {}
 //! # }
-//! # #[async_trait]
+//! # #[async_trait(512)]
 //! # trait Test2 {
 //!     // or
 //!     async fn test(elided: Elided<'_>) {}
@@ -209,9 +209,9 @@
 //! by value, no associated types, etc.
 //!
 //! ```
-//! # use async_trait::async_trait;
+//! # use stackfuture_async_trait::async_trait;
 //! #
-//! #[async_trait]
+//! #[async_trait(512)]
 //! pub trait ObjectSafe {
 //!     async fn f(&self);
 //!     async fn g(&mut self);
@@ -225,7 +225,7 @@
 //! #
 //! # struct MyType;
 //! #
-//! # #[async_trait]
+//! # #[async_trait(512)]
 //! # impl ObjectSafe for MyType {
 //! #     async fn f(&self) {}
 //! #     async fn g(&mut self) {}
@@ -263,16 +263,16 @@
 //! the default implementations are applicable to them:
 //!
 //! ```
-//! # use async_trait::async_trait;
+//! # use stackfuture_async_trait::async_trait;
 //! #
-//! #[async_trait]
+//! #[async_trait(512)]
 //! pub trait ObjectSafe: Sync {  // added supertrait
 //!     async fn can_dyn(&self) {}
 //! }
 //! #
 //! # struct MyType;
 //! #
-//! # #[async_trait]
+//! # #[async_trait(512)]
 //! # impl ObjectSafe for MyType {}
 //! #
 //! # let value = MyType;
@@ -284,9 +284,9 @@
 //! bounding them with `Self: Sized`:
 //!
 //! ```
-//! # use async_trait::async_trait;
+//! # use stackfuture_async_trait::async_trait;
 //! #
-//! #[async_trait]
+//! #[async_trait(512)]
 //! pub trait ObjectSafe {
 //!     async fn cannot_dyn(&self) where Self: Sized {}
 //!
@@ -295,7 +295,7 @@
 //! #
 //! # struct MyType;
 //! #
-//! # #[async_trait]
+//! # #[async_trait(512)]
 //! # impl ObjectSafe for MyType {}
 //! #
 //! # let value = MyType;
@@ -314,8 +314,7 @@
     clippy::similar_names,
     clippy::too_many_lines
 )]
-
-extern crate proc_macro;
+#![deny(rust_2018_idioms)]
 
 mod args;
 mod expand;
@@ -334,6 +333,6 @@ use syn::parse_macro_input;
 pub fn async_trait(args: TokenStream, input: TokenStream) -> TokenStream {
     let args = parse_macro_input!(args as Args);
     let mut item = parse_macro_input!(input as Item);
-    expand(&mut item, args.local);
+    expand(&mut item, args.local, &args.stack_size);
     TokenStream::from(quote!(#item))
 }

src/parse.rs

@@ -8,7 +8,7 @@ pub enum Item {
 }
 
 impl Parse for Item {
-    fn parse(input: ParseStream) -> Result<Self> {
+    fn parse(input: ParseStream<'_>) -> Result<Self> {
         let attrs = input.call(Attribute::parse_outer)?;
         let mut lookahead = input.lookahead1();
         if lookahead.peek(Token![unsafe]) {